There are various approaches for providing traffic signal priority for emergency vehicles (hereinafter referred to as “preemption”) at an intersection. One approach uses strobe lights to activate optical receivers at the intersection. Another approach uses noise pattern recognition to preempt based on approaching sirens. Recent preemption systems make use of global positioning system (GPS) technology to predict the approach of the emergency vehicles at the intersection.
All of the above approaches, however, have their drawbacks. Strobe-based preemption generally requires an optical line-of-sight which may be obstructed by hills, turns, and the like. Furthermore, strobe-based preemption requires expensive receiver units and installation of the strobe lights and related equipment in the cars. The range of strobe-based preemption may also be limited to only a few hundred feet.
The drawbacks of preemption based on siren noises is that such noises may or may not be recognized depending on their direction and distance from the intersection. Their recognition may also be obstructed by ambient noises, such as, for example, traffic sounds, horns, and the like.
The drawbacks of a GPS-based preemption system is that the installation of the GPS devices in the emergency vehicles may be expensive. Even if installed, GPS position data may not always be readily available. For example, although GPS systems are effective in providing position data in light metropolitan and rural areas, such positions may be occluded by buildings, bridges, and the like, in large cities. GPS systems may also not be available during emergencies such as, for example, a terrorist event. GPS receivers are also more susceptible to jamming than most receivers. Nonetheless, a GPS preemption system, when available, is very effective in terms of timing and vehicle position determinations.
Accordingly, what is desired is a preemption system and method that helps overcome the drawbacks of prior preemption systems.